The identification of small organic molecules that affect specific biological functions is an endeavor that impacts both biology and medicine. Such molecules are useful as therapeutic agents and as probes of biological function. In but one example from the emerging field of chemical genetics, in which small molecules can be used to alter the function of biological molecules to which they bind, these molecules have been effective at elucidating signal transduction pathways by acting as chemical protein knockouts, thereby causing a loss of protein function. (Schreiber et al. J. Am. Chem. Soc. 1990, 112, 5583; Mitchison, Chem. and Biol. 1994, 1, 3) Additionally, due to the interaction of these small molecules with particular biological targets and their ability to affect specific biological functions, they may also serve as candidates for the development of therapeutics.
Because it is difficult to predict which small molecules will interact with a biological target, intense efforts have been directed towards the generation of large numbers, or “libraries”, of small organic compounds. These libraries can then be linked to sensitive screens to identify the active molecules. In many cases, researchers have developed “biased” libraries, in which all members share a particular characteristic, such as an ability to interact with a particular target ligand, or a characteristic structural feature designed to mimic a particular aspect of a class of natural compounds. For example, a number of libraries have been designed to mimic one or more features of natural peptides. Such peptidomimetic libraries include phthalimido libraries (WO 97/22594), thiophene libraries (WO 97/40034), benzodiazopene libraries (U.S. Pat. No. 5,288,514), libraries formed by the sequential reaction of dienes (WO 96/03424), thiazolidinone libraries, libraries of metathiazanones and their derivatives (U.S. Pat. No. 5,549,974), and azatide libraries (WO 97/35199) (for review of peptidomimetic technologies, see Gante, J., Angew. Chem. Int. Ed. Engl. 1994, 33, 1699–1720 and references cited therein).
Each of these libraries has provided solid phase synthetic strategies for compounds possessing specific core functionalities, but none achieves the complexity of structure found in natural products, or in other lead compounds prepared through traditional chemical synthetic routes. Complex natural products commonly contain several different functionalities and often are rich in stereochemical complexity. Such diversity and complexity are difficult to achieve if the synthesis is restricted to a specific class of compounds.
Recognizing the need for development of synthetic strategies that produce large numbers of complex molecules, Boger et al. (EP 0774 464) have recently developed a solution-phase synthetic strategy for producing a library of compounds based on a functionalizable template core, to which various reagents can be added. However, there remains a need for development of solid-phase strategies, where the more rapid production methods such as split-and-pool strategies can be employed to generate larger (>1,000,000), more complex libraries. Additional solution-phase strategies would, of course, also be valuable.